In quartz veins, gold accumulates into large chunks after each earthquake, potentially weighing up to 60kg.
Natural gold forms within quartz – the second most abundant mineral in the Earth’s crust, after feldspar. Unlike other types of gold deposits, gold in quartz typically concentrates into large masses. In a new study published in the journal Nature Geoscience on September 2, a team of scientists discovered that earthquakes stimulate quartz to create large gold formations, solving a mystery that has persisted for decades.
Gold formations inside quartz veins – cracks in the rock filled with mineral-rich hydrothermal solutions. (Photo: Henri Koskinen)
Hydrothermal solutions carry gold atoms from deep underground and push them through quartz veins, meaning that theoretically, gold should be evenly distributed in the cracks rather than concentrated into lumps, according to Chris Voisey, a geologist at Monash University and the lead author of the new study. These large chunks are particularly valuable and account for up to 75% of all the gold ever mined.
Voisey noted that there were two clues that helped him and his colleagues unravel the mystery of the gold deposits. First, the largest chunks appear in tectonic gold mines – mines formed during earthquakes. Second, quartz is a piezoelectric mineral, meaning it generates an electric charge under geological pressure, such as the pressure caused by earthquakes.
The research team found that earthquakes fracture rocks and push hydrothermal solutions into quartz veins, filling them with dissolved gold. Under the pressure of an earthquake, quartz veins generate an electric charge that reacts with gold, causing the gold to cluster and solidify.
“Gold concentrates in certain locations because dissolved gold in the solution preferentially clumps onto pre-existing gold particles. Essentially, gold acts as an electrode for subsequent reactions by receiving the voltage generated by nearby quartz crystals,” Voisey explained.
This means that in quartz veins, gold solidifies into larger chunks after each earthquake. Voisey mentioned that the largest tectonic gold chunks found to date weigh around 60kg.
To test their theory, the research team simulated the effects of earthquakes on quartz crystals in the laboratory. They immersed the crystals in a gold-containing solution and recreated seismic waves to generate piezoelectric charges. The experiment confirmed that under geological pressure, quartz can generate a voltage sufficient to cause dissolved gold to cluster, while also confirming that gold tends to cluster on pre-existing gold ores, explaining the formation of large gold chunks.
In addition to deciphering the mystery behind the formation of large gold chunks, the new study could also help scientists create them in the laboratory. “But this is not alchemy. You need to have gold in solution, and then you just need to transfer it from a dissolved state to adhering to something else,” Voisey said.
